1. Field of the Invention
The present invention relates to a key-top sheet for a push button switch, and in particular to an in-mold type keytop sheet using a film.
2. Description of the Background Art
Generally, a push button switch is used as a control panel for an electronic device. A keytop sheet of the push button switch is fabricated based on a molding process and a silk printing process. In order to fabricate the keytop sheet, there are provided an upper mold having a plurality of cavities for forming a keytop and a lower mold having a cavity for forming a frame and a pushing portion. In this state, the upper mold and the lower mold are engaged, and a high temperature and pressure transparent injection material such as polycarbonate, resin, etc is implanted into an underside of the lower mold via a pin gate provided on the underside. As a result, as shown in FIG. 1, the keytop sheet becomes one part by connecting a plurality of keytops 2, for example, 15 keytops(in the case of a telephone, 12 keytops) via a connection rib 1(hereinafter called as runner) based on the molding process.
When the keytops 2 are formed by the molding process, a silk printing process is performed. In this case, a keytop sheet is generally fabricated by printing a certain character or numeral number on an underside of each keytop 2 which are processed based on the molding process. At this time, the silk printing is performed more than twice. Generally, the number of the silk printing is determined depending on the number of printing colors. As shown in FIG. 2, a keytop sheet 3 having a structure in which a plurality of keytops are connected by the runner 1 is fabricated.
The runner 1 connects a plurality of keytops during a molding process and forms the keytops as one part. Since the runner is formed of the same material as the keytops, namely, a transparent injection material, the elasticity of the runner is not good. In addition, a user pushes a certain keytop in a state that the completed keytop sheet is inserted into a product, since the keytops are connected by the runner, neighboring keytops are slightly pushed. Therefore, when the conventional keytop sheet is actually adapted to a product, there is a problem in that a tactile feel(a feel when a user pushes a button) is decreased.
In addition, as shown in FIG. 3, in the conventional keytop sheet, the runner has a thickness of about 0.8xcx9c1.2 mm. Therefore, when the keytop sheet is actually adapted to a product, the entire thickness of a product is increased due to the thickness (1.2 mm) of the runner.
Furthermore, in the conventional art, since a silk printing process is additionally required when fabricating the keytop sheet, the cycle time of the keytop sheet is increased. The number of the silk printing process is increased depending on the number of printing colors. Therefore, the defected products may be increased due to the increased number of printing processes.
Accordingly, it is an object of the present invention to provide an in-mold type keytop sheet which is capable of enhancing a reliability and productivity of a product by performing a molding process for a keytop by inserting a previously silk-printed thin film into a mold.
It is another object of the present invention to provide an in-mold type keytop sheet which is capable of decreasing the thickness and weight of a product using a thin film as a rib for connecting keytops.
It is still another object of the present invention to provide an in-mold type keytop sheet which makes it possible to enhance a tactile feel of a user by connecting a plurality of keytops by a thin film.
To achieve the above objects, there is a provided an in-mold type keytop sheet which is implemented by connecting a plurality of keytops using a film based on a molding process for the keytops after a previously silk-printed thin film into a mold.
Additional advantages, objects and features of the invention will become more apparent from the description which follows.